Content-based coding, which independently codes the objects included in a picture, has recently attracted considerable attention for its property of enabling object-based editing of still and motion pictures. In content-based coding, it is required to code arbitrarily shaped objects. Therefore, it is necessary to apply 2D-DCT to 8 X 8 blocks that include object boundaries. Padding is a technique that enables condign of such blocks by assigning imaginary values to the pixels that are not included in the object. Additionally, padding prevents the increase of the high frequency DCT coefficients which is caused by the discontinuous object boundary. In this paper, a new padding method named Symmetric Padding, which provides high coding efficiency with a simple copy-and-paste procedure, is proposed. Additionally a content-based 2D-DCT coding method, which changes the padding method and the scanning method according to the features of the object shape, is proposed. Due to the increase of the number of zero DCT coefficients, the proposed method shows better coding performance than conventional method, especially, at high bit rates.